Glow-discharge microphone



g. 16, P THOMAS GLOW. mscmmes uicnornoun 'Filedlarch 24. 1924 WITNESSES: INVENTOR Patented Aug. '16, 1927.

UNITED STATES J 1,638,893 PATENAT'IOFFICE.

PHILLIPS THOMAS, OI EDGEWOOD, PENNSYLVANIA, ASSIGNOR' TO WESTINGHOUSE ELECTRIC & MANUFACTURING COMPANY, A CORPORATION OF PENNSYLVANIA.

GLOW-DISCHARGE MICROPHONE.

Application filed March 24, 1924. Serial No. 701,298.

My invention relates to telephone systems and apparatus and it has particular reference to sound-wave translating devices.

One object of my invention is to provide an im roved translating device for converting vi ratory motion in a fluid medium into vibratory electric currents. Another object of my invention is to provide a microphone device whereby sound waves are more easily translated into correspondingly modulated electrical energy.

Another object of my invention is to provide a telephonic translating device which shall be eharacterizedby its simplicity of design and operation, and which lends itself to inexpensive production.

Another object of my invention is to provide a telephonic translating device which shall be of greatly increased sensitivity.

Another object of my invention is .to provide a telephonic translating device of the glow-discharge type wherein the intensity of response to pressure variations is substantially independent of the frequency of such variation.

As disclosed in my co-pending application Serial- No. 600,822, filed November 14, 1922. glow discharge transmitter, a glow discharge maintained between electrodes manifests a variety of characteristics by which var ous portions can be recognized. These portlons comprise a positive or anode column 1n contact with the positive electrode, and, following in sequence toward the negative electrode, a Faraday dark space, a negative light, a cathode darkspace and a cathode glow, which latter is in contact with the negative electrode. I have found that'the voltage current characteristic of this glowdischarge varies with the pressure of the surrounding fluid medium.

In the practice of my invention, I provide a pair of mounted electrodes, a chamber surrounding the positive electrode, a source of steady direct current and a means for amphfying the vibratory currents produced by the change in current voltage characteristic of the glow-discharge with change 1n pressure. In my co-pending application No. 688,379, filed January 27, 1924., I disclose a type of glow-discharge transmitter having a pair o electrodes as just described between which is maintained, by suitable means, a glowdischarge having a positive column and a chamber surrounding a positive column.

In order to insure that the discharge will be a glow discharge and will continue to be a glow discharge and not change into an are, I find that the source of potential must be high and that a current limiting device must be used. In one specific embodiment of my invention I employed a source of somewhat more than 4000 volts with a resistance in series between it and the discharge device of approximately one megohm. In another specific embodiment of this invention I em ployed a source of 4200 volts together with a current limiting device which restricted the current to one millimeter. The current limiting device used in this instance was a saturation tube.

A characteristic difierence between the glow discharge and the arc is found in the relation of current to voltage. In the are the current is much greater and the voltage much smaller than in the. glow discharge. Another characteristic difference is that with the glow discharge the electrodes are relatively cool, never becoming incandescent, while with an arc the electrodes are hot and the cathode is usually more incandescent than any portion of the arc itself.

I have found that the whole of the glow discharge is sensitive to sound variations. I have further found that this sensitivity may be greatly increased by surrounding the os1- tive electrode with a chamber. This 0 amber is also made to enclose the positive column of the glow-discharge and a small opening is provided for the passage of the current between the electrodes. This construction produces a glow-discharge transmitter of high sensitivity and one of approximately uniform sensitivity to all vibration frequencies. The sensitivity of the glow-discharge transmitter constructed according to my invention is greater than that of the ordinary carbon grain microphone and it gives far more uniform response to various frequencies.

I have found that this chamber markedly accentuates the sensitivity of the glow-discharge to the sound vibrations. I have further found, however, that this chamber may have a definite but very high resonant fre-' quency which causes it, not only to accentuate the response to vibrations of all frequencies, but to accentuate undul the response to the frequency to which t e chamber is resonant. I have found that by partially filling the chamber with a sound absorbcnt means, s ecifically, partly filling the chamber with fe t, I am able to subdue the resonance phenomena and to retain the accentuation of sound response. The accentuation then remains constant fer all sound frequencies.

The gain in sensitivity and in accuracy of translation produced by my invention over other constructions enables me to obtain a sufliciently large telephonic frequency current of satisfactory faithfulness of translation, for such applications as the modulation of the radio frequency output of a radiosendi-ng apparatus, and to obtain it through the agency of alesser number of stages of amplification than has hcretofore'been required.

other objects and applications of my invention', as well as structural details, will be apparent from the following description when read in connection with the accompanying drawing, wherein:

The single figure is a diagrammatic view of circuits and apparatus embodying my invention.

In the figure is shown a glow-discharge transmitter capsule 1, a source of high voltage direct current 2 and an amplifier assembly 3.

The glow-discharge transmitter capsule 1 comprises a cylindrical supporting portion 4, a positive electrode 5 mounted in a screw 6, and a negative electrode 7 also mounted in a screw 8. The screw 8 is held in place by nuts 9 and 10 within and without the cylinder of the capsule 4. The screw 6 carrying electrode 5 is held in place partly by nut 11. A cup-piece 12 is also provided having a threaded hole through the bottom thereof which also aids in holding screw 6 in position. Arecess or chamber is formed in the cup-piece 12 which is covered by a top plate 14 held in place by a wire spring fastener 15. The cover plate 14 has a hole 16 in the center thereof, which, by the construction shown, brings the hole 16 into the line be tween electrodes 5 and 7. The chamber formed in the cup-piece 12 is partly filled by a felt-cylinder 17, the hole through its center serving to accommodate electrode 5 and screw 6. Conductors 18 and 19 conduct current to electrodes of the glow-discharge capsule 1 from the source 2. They also connect the device 1 to the electrodes of ampli- It has not been possible as yet to determine the precise mode (if-operation of this modification of the glow-discharge transmitter. From the information at present available, it is believed that the increase in sensitivity obtained by the addition of cup 12 and cover 14 is due to an air blast in and out through the hole 16 in the cover 14 caused by pressure changes in the surrounding atmosphere.

as just described.

It is probable that this air blast'afl'ects ducesa very marked increase in the semi-- positive column to accentuate the, voltage);

tivity and response of the glow-discharge to the vibratory influence of sound waves. Otherwise, the action of'the transmitter is, in general, similar to that described in my co-pending application previously mentioned.

The felt filler 17 serves as a means for preventing the resonance within the chamber of the cup-piece 12 without rcdueing,'to any great extent, the volumetric capacity of the chamber. The addition of felt 17 therefore, by its damping action destroys the natural resonance of the chamber in the cuppiece 12 withoutdestroying the effect which an air blast in and out thereofproduces upon the positive column of the glow-discharge In view of the foregoing, my invention provides means for producing a marked increase in the sensitivity and response of a glow-discharge transmitter as compared to one made according to previous systems of construction and avoids the effects of natural resonance phenomena to specific sound frequencies in the device.

'While I have shown only one embodiment of my invention in the accompanying drawings, it is capable of various changes and 'modifications therefrom without departing 1. In combination, a pair of spaced elec trodes respectively positive and negative, means for establishing a glow-discharge therebetween, a chamber enclosing said positive electrode and sound'resonance preventng means in sa1d chamber.

2. In combination, a pair of spaced electrodes respectively positive and negative, means for establishing a glow-d1scharge 'therebetween, an amplifier means connected thereto and means enclosing said positive,

electrode and having a sound deadening device therein. 3. A sound-translating device comprising a pair of spaced electrodes, means for establishing a glow-discharge therebetween including a positive column, and a member surrounding said positive column and having a single opening therein positioned between said electrodes, and a sound absorbent means within said member.

4. A sound-translating device comprising in combination a pair of electrodes constituting the positive and negative terminals of adischarge device, means for establishing a glow-discharge therebetween having a positive column and having a voltage-current characteristic which changes with change in pressure, and means comprising a member surrounding said positive column for increasing said change in voltage-current characteristic with change in pressure and having sound damping means therein.

5. A glow-discharge sound-responsive device comprising a pair of electrodes, a supporting means therefor, means inclosing one of said electrodes, and sound damping means for destroying the natural resonance of said inclosing means.

6. A glow-discharge sound-responsive device comprising a positive electrode and a negative electrode, supporting means for positioning said respective electrodes, means non-resonant to sound for enclosing said positive electrode, and means for estab lishing a glow-discharge between said electrodes.

7. A sound translating system comprising a sound-responsive apparatus and an amplifying device, said sound-responsive apparatus comprising a glow-discharge transmitter having a positive electrode and a negative electrode, supporting means for positioning said respective electrodes, amember surroundin said positive electrode, means for destroying the sound resonance of said surrounding member, means for establishing a glow-discharge between said electrodes, sa1d amplifying means comprising a thermionic dischargedevice having a cathode, an

I anode and a control electrode, a high resistance conductor connecting said control electrode to said cathode, said cathode being also connected to an electrode of said transmitter, said control electrode being capacitively connected to said other electrode of said transmitter, and an output means, and a source of current respectively connected between said cathode and said anode. 1

8. In a glow-discharge sound-responsive device comprising a posltive and a negative electrode, a sound accentuating chamber surrounding said positive electrode and sounddamping means within said chamber.

9. In a glow-discharge sound-responsive device comprising a positive and a negative electrode, and means for producinga glowdischarge therebetween, a chamber surrounding said positive *electrode and sound damping means therein, the dimensions of said chamber bein less than the length of the shortest soun wave to which it is intended to respond and greater than the average ex-- cursion of a particle of air produced by successive sound waves.

10. In a glow-discharge sound-responsive device. comprising a positive electrode, a negative electrode and means for producing a glow-discharge therebetween having a posltive column, and means for intensifying the response of said positive column to sound, said means comprising a chamber surrounding said positive column and said positive electrode, and sound-damping means therein.

11. A glow-discharge sound-responsive device comprising a positive electrode and a negative electrode, means for producing a glow-discharge therebetween, comprising a source of high voltage direct current, sup porting means of insulating material for said electrodes so spacing them as to allow the passage of said glow-discharge, a chamber surrounding said positive electrode, said chamber comprising a non-conducting cup having a bottom that is drilled and tapped for the passage of said positive electrodes, a metallic cover closing the top opening of said cup, said cover having an opening for the passage of said glow-discharge, and a sounddamping means comprising a felt filler portion.

12. A translating device comprising a pair of spaced electrodes, means for establishing a glow-discharge having a positive column therebetween and a chamber surrounding said positive column, said chamber having a single opening thereto that is adapted and positioned for the passage of the glow-discharge therethrough, and sound absorbent means therein comprisin a felt filler member.

13. A glow-disc arge sound-responsive device comprising a positive electrode and a negative electrode, supporting means for po-' sitioning said respective electrodes, means non-resonant to sound for enclosing said ositive electrode, the negative electrode bemg outside said enclosing means, and means for establishing a glow-discharge between said electrodes.

In testimony whereof, I have hereunto subscribed my name this 14th day of March,

PHILLIPS THOMAS. 

